FOEMATION OF SEA-ICE. 85 



CHAPTEE V. 



FORMATION OP ICE.-ICE-FLOES, FIELDS OF ICE, AND ICEBERGS. -ICE IN THE 

 BALTIC AND THE BLACK SEA. 



In the Polar seas tlie low temperature results in tlie formation of 

 ice During tlie long winters of these cold regions, the tranquil 

 water of the bays and gulfs freezes round the edge of the coasts, and 

 the crystallized.mass gaining incessantly on the sea finally extends 

 to a considerable distance. This is " ground-ice.'' The surface of the 

 sea disappears like that of the lakes under a soHd layer; but the 

 manner of forming the icy crust differs, for in the rivers and basins 

 of fresh water, crystals of ice at first appear over almost the entire 

 surface, but in the seas which have no great depth it is generally 

 from the bed itself that the liquid mass congeals. ^ 



In fact, salt water has not, like fresh water, its greatest, density 

 at the temperature of 39-2 degrees Fahr., but it becomes hea- 

 Tier and heavier in proportion as it freezes. The coldest strata of 

 water, being also the heaviest, descend vertically towards the bottom 

 of the sea, and displace the lower strata, which are lighter and of a 

 higher temperature. While the water which descends to the bottom 

 in rivers has a normal heat of seven degrees above freezmg-pomt, 

 the sea-water which falls deeper may have been chilled to 6Z 

 Fahr or even many degrees below it. When the mass is not 

 agitated, it remains liquid, but, on the slightest disturbance it 

 suddenly turns to ice. Sometimes, at the commencement of winter, 

 the mariners and fishermen of the Baltic and western coasts of Nor- 

 way find themselves suddenly surrounded by floes of ice, which rise 

 from the bed of the sea and which still contain fragments of lucus. 

 It appears so rapidly that the boats often run great risk of being 

 crushed between the solid masses which are piled around them, and 

 the crews are in imminent danger. Around the rocky coasts of 

 Greenland, Labrador, and Spitzbergen, these ice-floes often raise huge 

 stones which they have torn from the bed of the sea.* 



i 



Edlund, Poggendorfs Annalen, cxxi. 

 D 2 



